PURPOSE: To evaluate the effect of high-frequency jet ventilation (HFJV) and continuous positive airway pressure (CPAP) on oxygenation and the shunt fraction (Qs/Qt) during one-lung ventilation (OLV). METHODS: Twenty-five patients who were undergoing resection of a descending aortic aneurysm were studied. Arterial oxygenation, Qs/Qt, and hemodynamics were evaluated just before the initiation of OLV (T1), 15 min after OLV (T2), and 15 min (T3) and 30 min (T4) after the application of HFJV or CPAP to the nondependent lung. RESULTS: There were no significant changes in the mean arterial blood pressure (MAP), heart rate (HR), central venous pressure (CVP), or mixed venous partial pressure of oxygen throughout this study. The arterial partial pressure of oxygen (Pa(O2)) values after the application of HFJV or CPAP increased significantly, from 173.8 +/- 39.6 mmHg (T2) to 344.1 +/- 87.9 mmHg (T3) and 359.9 +/- 82.4 mmHg (T4) in the HFJV group (P < 0.05), and from 153 +/- 38.5 mmHg (T2) to 243 +/- 48.5 mmHg (T3) and 249.7 +/- 55.0 mmHg (T4) in the CPAP group (P < 0.05). The shunt fraction decreased significantly after the initiation of HFJV or CPAP, from 38.7% +/- 8.9% (T2) to 27.0% +/- 8.0% (T3) and 25.9% +/- 8.7% (T4) in the HFJV group (P < 0.05), and from 44.6% +/- 8.6% (T2) to 34.3% +/- 10.2% (T3) and 32.6% +/- 8.5% (T4) in the CPAP group (P < 0.05). The arterial saturation of oxygen (Sa(O) (2)) increased significantly after the application of either HFJV or CPAP (P < 0.05). CONCLUSIONS: Both HFJV and CPAP can improve oxygenation during OLV.